Background art of this technical field includes PTL 1 that relates to a nanopore Raman DNA sequence. This publication discloses technology that causes biopolymers to approach a nanopore having an inner diameter of approximately 10 nm so as to increase excitation light with which the nanopore is irradiated and Raman scattered light of the biopolymers which pass through the nanopore, with the scattered light produced through conductive thin film provided in the vicinity of the nanopore, and then that detects the excitation light and scattered light and measures the biopolymers. Therefore, it is necessary to continuously hold a portion as an observation object at a fixed position with accuracy of tens to hundreds of nanometers, although a diameter of an irradiation spot of the excitation light is an important factor.
PTL 2 discloses another type of technology that relates to such fixed position control. In addition, PTL 3 discloses still another type of technology that detects and corrects a positional shift due to a temperature change.